#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <poll.h>
#include "asoundlib.h"
      
snd_pcm_t *playback_handle;
short buf[4096];

int playback_callback(snd_pcm_sframes_t nframes)
{
	int err;

	printf("playback callback called with %d frames\n", (int)nframes);

	// Write number of frames of data in buf interleaved to playback stream
	if ((err = snd_pcm_writei(playback_handle, buf, nframes)) < 0)
	{
		fprintf(stderr, "write failed (%s)\n", snd_strerror (err));
	}

	return err;
}
      
int main (int argc, char *argv[])
{
	snd_pcm_hw_params_t *hw_params;
	snd_pcm_sw_params_t *sw_params;
	snd_pcm_sframes_t frames_to_deliver;
	int err;
	unsigned int val = 16000; // 44100;
	int dir;

	if ((err = snd_pcm_open(&playback_handle, argv[1], SND_PCM_STREAM_PLAYBACK, 0)) < 0)
	{
		fprintf(stderr, "cannot open audio device %s (%s)\n", argv[1], snd_strerror (err));
		exit (1);
	}
	   
	if ((err = snd_pcm_hw_params_malloc(&hw_params)) < 0)
	{
		fprintf(stderr, "cannot allocate hardware parameter structure (%s)\n", snd_strerror (err));
		exit (1);
	}
			 
	if ((err = snd_pcm_hw_params_any(playback_handle, hw_params)) < 0)
	{
		fprintf(stderr, "cannot initialize hardware parameter structure (%s)\n", snd_strerror (err));
		exit (1);
	}

	if ((err = snd_pcm_hw_params_set_access(playback_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0)
	{
		fprintf(stderr, "cannot set access type (%s)\n", snd_strerror (err));
		exit (1);
	}

	if ((err = snd_pcm_hw_params_set_format(playback_handle, hw_params, SND_PCM_FORMAT_S16_LE)) < 0)
	{
		fprintf(stderr, "cannot set sample format (%s)\n", snd_strerror (err));
		exit (1);
	}

	if ((err = snd_pcm_hw_params_set_rate_near(playback_handle, hw_params, &val, &dir)) < 0)
	{
		fprintf(stderr, "cannot set sample rate (%s)\n", snd_strerror (err));
		exit (1);
	}

	if ((err = snd_pcm_hw_params_set_channels(playback_handle, hw_params, 2)) < 0)
	{
		fprintf(stderr, "cannot set channel count (%s)\n", snd_strerror (err));
		exit (1);
	}

	if ((err = snd_pcm_hw_params(playback_handle, hw_params)) < 0)
	{
		fprintf(stderr, "cannot set parameters (%s)\n", snd_strerror (err));
		exit (1);
	}

	snd_pcm_hw_params_free(hw_params);

	// tell ALSA to wake us up whenever 4096 or more frames
	// of playback data can be delivered. Also, tell
	// ALSA that we'll start the device ourselves.
	if ((err = snd_pcm_sw_params_malloc(&sw_params)) < 0)
	{
		fprintf(stderr, "cannot allocate software parameters structure (%s)\n", snd_strerror (err));
		exit (1);
	}

	if ((err = snd_pcm_sw_params_current(playback_handle, sw_params)) < 0)
	{
		fprintf(stderr, "cannot initialize software parameters structure (%s)\n", snd_strerror (err));
		exit (1);
	}

	if ((err = snd_pcm_sw_params_set_avail_min(playback_handle, sw_params, 4096)) < 0)
	{
		fprintf(stderr, "cannot set minimum available count (%s)\n", snd_strerror (err));
		exit (1);
	}

	if ((err = snd_pcm_sw_params_set_start_threshold(playback_handle, sw_params, 0U)) < 0)
	{
		fprintf(stderr, "cannot set start mode (%s)\n", snd_strerror (err));
		exit (1);
	}

	if ((err = snd_pcm_sw_params(playback_handle, sw_params)) < 0)
	{
		fprintf(stderr, "cannot set software parameters (%s)\n", snd_strerror (err));
		exit (1);
	}

	// the interface will interrupt the kernel every 4096 frames, and ALSA
	// will wake up this program very soon after that.
	if ((err = snd_pcm_prepare(playback_handle)) < 0)
	{
		fprintf(stderr, "cannot prepare audio interface for use (%s)\n", snd_strerror (err));
		exit (1);
	}

	while (1)
	{
		// wait till the interface is ready for data, or 1 second has elapsed.
		if ((err = snd_pcm_wait(playback_handle, 1000)) < 0)
		{
			fprintf(stderr, "poll failed (%s)\n", strerror (errno));
			break;
		}	           

		// find out how much space is available for playback data
		if ((frames_to_deliver = snd_pcm_avail_update(playback_handle)) < 0)
		{
			if (frames_to_deliver == -EPIPE)
			{
				fprintf(stderr, "an xrun occured\n");
				break;
			}
			else
			{
				fprintf(stderr, "unknown ALSA avail update return value (%d)\n", (int)frames_to_deliver);
				break;
			}
		}

		frames_to_deliver = frames_to_deliver > 4096 ? 4096 : frames_to_deliver;

		// deliver the data
		if (playback_callback(frames_to_deliver) != frames_to_deliver)
		{
			fprintf(stderr, "playback callback failed\n");
			break;
		}
	}

	snd_pcm_close (playback_handle);
	exit (0);
}
